Mechanism Of Utilization Of Urea Nitrogen In The Diet Of Rabbits And It's Application

Present research was conducted to study the digesting, absorpting and utilizing ability and metabolic pathway of urea-N in rabbits, and to provide a theory for the effective and safety utilization of urea-N in rabbit diet. Three series of research were included in this study as follows:1 Studies on Absorption , Digestion and Utilization of Urea by Using 15N-urea in RabbitsMale New Zealand White rabbits weighted 2.5kg and aged 3 months were used in this experiment. Studing nitrogen balance value of urea, determining apparent digestibility and utilization coefficient and analyzing protein nitrogen and nonprotein nitrogen in the rabbits were carried out through the metabolism of l5N labelled urea in rabbit body by using 15N tracer technique under the three different conditions (normal, caecectomia and coprophagy-prevented). The basal diet contained 16% of curde protein was fed to the rabbits for 120 g per day with 1% of additive 15N-urea(1.2000g). The results under three conditions (in normal rabbit, caecectomia rabbit and coprophagy-pre vented rabbit) were as follows: (1) Nitrogen balance value of urea in rabbits were 98.3+12.4, 93.4+0.2 and 38.1+1.3 mg per day respectively, which accout for 18.2 +1.85%, 17.2+0.5% and 7.2+1.8% of the 15N-urea intake respectively. (2)Apparent digestibility of urea-N were 87.8+1.4%, 91.4 + 0.2% and 85.5 + 6.7% respectively and utilization coefficient of urea-N were 20.7 +8.4%, 18.8 +5.4% and 8.0+0.4% respectively. (3)There were respectively 90.6%,89.2% and 72.2% of labelled 15N in protein nitrogen in the rabbits blood. (4)There were respectively 70.4%,63.8%;65.0%,29.4% and 9.8%,14.7% of labelled 15N in protein nitrogen in stomach and small intestine content. The mean labelled 15N in protein nitrogen in other organs (stomach, small intestine, caecum, large intestine, lever and deltoid) were respectively 74.1%,69.9% and 66.2%. (5)It was also observed that the 15N-urea could convert into form of protein in caecum content in normal and coprophagy-prevented rabbit which were respectively 78.5% and 64.4%. But apparent digestibility of theurea nitrogen is not much different, because it is easier to be decomposed. The true digestibility was likely to be higher. Although the nitrogen balance values in rabbits of 3 groups were all positive equilibrium among them, the difference were still singnificant, normal rabbits was the highest,the coprophagy-prevented rabbit was the lowest, and the caecectomia rabbit was slightly lower than normal rabbit. So did that of the utilization coefficient of urea-N. In the rabbit the utilization coefficient of urea nitrogen was as high as 20.7%, due to the effect of microflra in the caecum and behavour of coprophagy. Comaprison of normal rabbit to coprophagy prevented one the utilization coefficient of urea nitrogen, which is reduced to 8.8%, was 38.6% of normal rabbit, and avoirdupois of rabbit decrease. The utilization of urea nitrogen was resumed to the level of normal rabbits after one month underwent operation of caecectomia. Under above three different conditions (normal, caecectomia and coprophagy-prevented ), the proportion of lablled l3N of urea nitrogen which existed in the form of protein nitrogen were different between blood and organs but the former was higher due to having higher metabolic intensity in blood. The proportion of urea nitrogen lablled with l5N in the form of protein nitrogen in content of the caecum was the highest, which was reached to 78.5%, and it was obviously changed resulted from the metabolism of microorganism in caecum. The proportion of urea nitrogen lablled with 15N in the form of protein nitrogen in stomach and small intestine contents was lower by 86% and lower by 77% respectively in coprophagy-prevented rabbit compared with that of normal rabbit. This result suggested that content of stomach and small intestine came from partially caecum and gave a strong evidence of effect of microorganism in caecum on the nutrition of rabbits.2 Effects of urease inhibitor on utilization of urea-N in rabbits In this stu...